Phase Engineering Modulates the Electronic Structure of the IrO/MoS Heterojunction for Efficient and Stable Water Splitting.

The engineering of dual-functional catalytic systems capable of driving complete water dissociation in acidic environments represents a critical requirement for advancing proton exchange membrane electrolyzer technology, yet significant challenges remain. In this work, we investigate an IrO/MoS/CNT heterostructure catalyst demonstrating enhanced bifunctional performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under acidic conditions. Strategic incorporation of IrO into the MoS/CNT heterojunction induces a partial phase transformation from 2H to the metastable 1T configuration in MoS, thereby modulating the electronic structure of IrO and improving the catalytic performance for overall water splitting. The optimized IrO/MoS/CNT catalyst exhibited exceptional overpotentials of 9 mV (HER) and 182 mV (OER) at a current density of 10 mA cm in acidic media. Full-cell evaluations further confirmed its practical potential, showing a 1.47 V operation voltage that outperforms standard Pt/C||IrO counterparts by 120 mV. The experimental results revealed that the n-n heterojunction between IrO/CNT and MoS/CNT generates a built-in electric field, enhancing charge redistribution and electron transport. Moreover, density functional theory simulations further identify iridium centers as dominant catalytic loci, with a metastable 1T-MoS phase mediating charge equilibration at atomic interfaces. This modification facilitates *OH adsorption and *OOH deprotonation and lowers the kinetic barrier during the water-splitting process.